In the inventory control of products such as rental videos or CDs (compact discs), it is expected to identify, by using an RFID (radio frequency identification) system, the presence of video products or CD products which are placed on the product shelves.
In the RFID system, an IC tag card is attached to, for example, a package which wraps a video product or CD product and a loop antenna is installed on a product shelf on which the product is placed. Typically, the shape of the product shelf loop antenna is substantially rectangular as shown in FIG. 2.
The IC tag card is, for example, an integrated circuit comprising a thin, small film antenna coil, and communicates with the product shelf loop antenna which is installed on the product shelf by way of an inductive electromagnetic field by using the antenna coil.
However, for a better communication by way of the inductive electromagnetic field, it is desirable to place the antenna plane of the antenna coil of the IC tag card in parallel, or at least it is necessary to place it obliquely, with respect to the antenna plane of the product shelf loop antenna, such that the most possible numbers of magnetic fluxes which are generated from the product shelf loop antenna cross the antenna plane of the antenna coil. This is because if the antenna planes of the both loop antennas are perpendicular to each other, extremely small numbers of magnetic fluxes intersect thereby sufficient communication cannot be done.
In the case of a cube having a relatively large size in length, width and height such as a package of a video product, it is easy to attach an IC tag card to such as the bottom face of the cube, the surface which will be parallel with the product shelf when placed on the product shelf. However, in the case of a cube having a small size in length, width and height such as a case wrapping a CD product or DVD product, it is typically difficult to attach an IC tag to the bottom face of the cube which will be parallel with the product shelf, since the IC tag card itself has a certain degree of two-dimensional size. A need has arisen for implementing a product inventory control by an RFID system wherein an IC tag card can be attached to a product, even to such a small product.